1. Field of the Invention
The present invention relates generally to glass sheets and, more specifically, to a method for heating and forming a glass sheet.
2. Description of the Related Art
It is known to heat glass sheets using a "hearth" or "lehr". Generally, the lehr is a furnace and may be of a continuous roller-type, fixtured roller-type or gas-type. For example, a roller-type lehr has a plurality of rollers disposed beneath a plurality of radiant heaters. Typically, a glass sheet is placed inside the lehr where it is heated by conventional radiation, convection and conduction heat. The glass sheet is moved along the rollers at a predetermined rate which depends on the thermal conductivity of the glass sheet to reach a temperature in its forming range. When the glass sheet is at a temperature in its forming range, the heated glass sheet is formed to a predetermined configuration using a plurality of forming rollers to bend the glass sheet to a desired curvature. Once formed, the glass sheet is either quenched, annealed or tempered.
Although the above lehr and forming rollers have worked well to heat and form a glass sheet, they suffer from the disadvantage that the lehr must be long in length to allow the glass sheet to be heated at the predetermined rate. They also suffer from the disadvantage that the process capability is limited due to heating the glass sheet with only radiant heat. They further suffer from the disadvantage that the forming rollers are limited to a single radius capability at a time. As a result, there is a need in the art to heat a glass sheet quickly in a controlled manner and to form the glass to a predetermined configuration using forming rollers.